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                    <h1>getPrimaryKey实现</h1>
                    
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                         作者 Leeves
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                          日期 2019-11-17
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            getPrimaryKey实现
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                <h4 id="背景"><a href="#背景" class="headerlink" title="背景"></a>背景</h4><p>　　闲来无事，在普某，看到这个东东，遂后产生好奇。</p>
<figure class="highlight plain"><table><tr><td class="code"><pre><span class="line">Samples samples = new Samples();</span><br><span class="line">//获取主键id</span><br><span class="line">xxx.getPrimaryKey(samples);</span><br></pre></td></tr></table></figure>
<p>简单来描述一下， Samples为数据库映射实体，数据库id不为自增，通过 getPrimaryKey方法，传入得到主键id。</p>
<p>　　理论上是有个主键id表来保存主键滴，而且如果多个线程来取id值时，会产生线程问题。那么就肯定会有那个东东出现啦。</p>
<h4 id="查看"><a href="#查看" class="headerlink" title="查看"></a>查看</h4><p>　　于是呼，我打开class文件，果然，看到了么，有synchronized来修饰：<br><img src="" alt="源码"> </p>
<p><img src="" alt="相视一笑"> </p>
<hr>
<h4 id="实践"><a href="#实践" class="headerlink" title="实践"></a>实践</h4><p>　　上面这个东东，只适合在普某使用，那么我就要重写成符合当前主流框架。</p>
<p>　　以下的例子是：spring boot + mybaist。</p>
<p>贴上主要代码：</p>
<figure class="highlight plain"><table><tr><td class="code"><pre><span class="line">@Data</span><br><span class="line">@EqualsAndHashCode(callSuper = false)</span><br><span class="line">@Accessors(chain = true)</span><br><span class="line">public class Samples implements Serializable &#123;</span><br><span class="line"></span><br><span class="line">    private static final long serialVersionUID=1L;</span><br><span class="line"></span><br><span class="line">    @TableId(type = IdType.INPUT)</span><br><span class="line">    private Long sampleId;</span><br><span class="line">    </span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<figure class="highlight plain"><table><tr><td class="code"><pre><span class="line">@Component</span><br><span class="line">public class SequenceGenerator &#123;</span><br><span class="line"></span><br><span class="line">    @Autowired</span><br><span class="line">    private IUniqueTableService uniqueTableService;</span><br><span class="line"></span><br><span class="line">    private final Lock lock = new ReentrantLock();</span><br><span class="line"></span><br><span class="line">    /**</span><br><span class="line">     * 默认增长值：20</span><br><span class="line">     */</span><br><span class="line">    @Value(&quot;$&#123;sequence.grow.value:20&#125;&quot;)</span><br><span class="line">    public long defaultSequenceGrowValue;</span><br><span class="line"></span><br><span class="line">    /**</span><br><span class="line">     * 记录sequence数</span><br><span class="line">     */</span><br><span class="line">    private static Map&lt;String, Long&gt; sequenceMap = new HashMap&lt;&gt;();</span><br><span class="line"></span><br><span class="line">    public &lt;T&gt; void getPrimaryKey(T t) throws IllegalAccessException &#123;</span><br><span class="line"></span><br><span class="line">        Class&lt;?&gt; clazz = t.getClass();</span><br><span class="line">        Field[] fields = clazz.getDeclaredFields();</span><br><span class="line">        for (Field field : fields) &#123;</span><br><span class="line">            if (field.isAnnotationPresent(TableId.class)) &#123;</span><br><span class="line">                lock.lock();</span><br><span class="line">                try &#123;</span><br><span class="line">                    String sequenceName = clazz.getSimpleName().concat(&quot;.&quot;).concat(field.getName());</span><br><span class="line">                    Long nowSequence = sequenceMap.get(sequenceName);</span><br><span class="line">                    long nextSequence;</span><br><span class="line"></span><br><span class="line">                    //是否在缓存map中</span><br><span class="line">                    if (nowSequence == null) &#123;</span><br><span class="line">                        //查询主键表</span><br><span class="line">                        LambdaQueryWrapper&lt;UniqueTable&gt; queryWrapper = new LambdaQueryWrapper&lt;&gt;();</span><br><span class="line">                        queryWrapper.eq(UniqueTable::getName, sequenceName);</span><br><span class="line">                        UniqueTable uniqueTable = uniqueTableService.getOne(queryWrapper);</span><br><span class="line"></span><br><span class="line">                        //数据库没有记录，则初始化记录</span><br><span class="line">                        if (uniqueTable == null) &#123;</span><br><span class="line">                            uniqueTable = new UniqueTable();</span><br><span class="line">                            uniqueTable.setName(sequenceName);</span><br><span class="line">                            uniqueTable.setCode(defaultSequenceGrowValue);</span><br><span class="line">                            uniqueTableService.save(uniqueTable);</span><br><span class="line">                            nextSequence = 1L;</span><br><span class="line">                            nowSequence = 1L;</span><br><span class="line">                        &#125; else &#123;</span><br><span class="line">                            //数据库有记录，缓存中没有，则表示系统是重启后的</span><br><span class="line">                            nowSequence = uniqueTable.getCode();</span><br><span class="line">                            uniqueTable.setCode(nowSequence + defaultSequenceGrowValue);</span><br><span class="line">                            uniqueTableService.update(uniqueTable, queryWrapper);</span><br><span class="line">                            nextSequence = nowSequence + 1L;</span><br><span class="line">                        &#125;</span><br><span class="line"></span><br><span class="line">                    &#125; else &#123;</span><br><span class="line">                        //缓存达最大值，则增长</span><br><span class="line">                        if ((nowSequence % defaultSequenceGrowValue) == 0L) &#123;</span><br><span class="line">                            LambdaQueryWrapper&lt;UniqueTable&gt; queryWrapper = new LambdaQueryWrapper&lt;&gt;();</span><br><span class="line">                            queryWrapper.eq(UniqueTable::getName, sequenceName);</span><br><span class="line">                            UniqueTable uniqueTable = uniqueTableService.getOne(queryWrapper);</span><br><span class="line">                            uniqueTable.setCode(nowSequence + defaultSequenceGrowValue);</span><br><span class="line">                            uniqueTableService.update(uniqueTable, queryWrapper);</span><br><span class="line">                        &#125;</span><br><span class="line">                        nextSequence = nowSequence + 1L;</span><br><span class="line">                    &#125;</span><br><span class="line"></span><br><span class="line">                    //设置值</span><br><span class="line">                    field.setAccessible(true);</span><br><span class="line">                    field.set(t, nowSequence);</span><br><span class="line">                    sequenceMap.put(sequenceName, nextSequence);</span><br><span class="line">                    break;</span><br><span class="line">                &#125; catch (IllegalAccessException e) &#123;</span><br><span class="line">                    e.printStackTrace();</span><br><span class="line">                    break;</span><br><span class="line">                &#125; finally &#123;</span><br><span class="line">                    lock.unlock();</span><br><span class="line">                &#125;</span><br><span class="line">            &#125;</span><br><span class="line">        &#125;</span><br><span class="line">    &#125;</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>多线程测试使用：</p>
<figure class="highlight plain"><table><tr><td class="code"><pre><span class="line">@Test</span><br><span class="line">public void test() throws InterruptedException &#123;</span><br><span class="line">    Samples samples = new Samples();</span><br><span class="line">    for (int i = 0; i &lt; 40; i++) &#123;</span><br><span class="line">        new Thread(() -&gt; &#123;</span><br><span class="line">            sequenceGenerator.getPrimaryKey(samples);</span><br><span class="line">            System.out.println(samples.getSampleId());</span><br><span class="line">        &#125;, String.valueOf(i)).start();</span><br><span class="line">    &#125;</span><br><span class="line">    TimeUnit.SECONDS.sleep(5);</span><br><span class="line">    System.out.println(&quot;-------------------&quot;);</span><br><span class="line">    System.out.println(samples.getSampleId());</span><br><span class="line">&#125;</span><br></pre></td></tr></table></figure>
<p>测试截图：</p>
<p><img src="" alt="测试"> </p>
<p>当然，这里的锁你也可以换成<code>synchronized</code>。你可以自己把锁去掉，然后测试一下会有什么效果，手动狗头。</p>

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